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Barbiturate: Synthesefragen/Erfahrungen?

#1
Hey,
ich wollte mal die beiden Barbiturate Barbital und Amobarbital herstellen und hätte dazu ein paar Fragen:
Hat schon jemand hier Erfahrungen mit denen, bzw. Barbituraten generell gemacht? Ich finde leider nur rel. wenig zu Barbituraten im Internet.
Synthese hätte ich die von Barbital auf erowid befolgt: Hier.
Könnte man da das Benzol bei der Veresterung zu Diethylmalonat durch ein anderes Lösungsmittel wie z.B. Xylol ersetzen?
Und die Synthese ist ja für Barbital, aber wenn ich bei der Herstellung von Diethyl-diethylmalonat die zweiten 65g Ethylbromid durch Isoamylbromid ersetze, sollte Amobarbital am Ende rauskommen, oder? (https://upload.wikimedia.org/wikipedia/c...thesis.png)
Schonmal vielen Dank im Vorraus für eure Antworten,
mfg Karl_der_Käfer
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#2
Mal was über Barbiturate wirklich sehr interessant  Wink
Also mit der Herstellung des Diethylmalonsäurediethylesters bist du bereits auf den richtigen Weg mit dem Ethylbromid. Würde das auch verdammt gerne herstellen, weiß nur nicht woher ich das Ethylbromid herbekomme.  Dodgy
Jedenfalls freu ich mich auch weitere Berichte bezüglich deiner Synthese. Wink
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#3
Ethylbromid lässt sich zuverlässig aus Ethanol NaBr und H2SO4 herstellen

ich zitiere:

Ethyl bromide is a clear, colorless liquid with a solvent-like smell much like that of ether. It is a potent ethylating agent, since it gives up the bromide easily. Whenever making this chemical, make sure to use ice cold water in any condensers. Don't use faucet water as it is usually not cold enough to efficiently condense ethyl bromide (Unless your faucet squeezes out ice cubes while its running). It is typically made from the action of a mixture of sulfuric acid and sodium bromide on ethanol or hydrobromic acid on ethanol. The latter will not be discussed as hydrobromic acid is extremely hard to get.

The reaction proceeds as follows:

H2SO4 + NaBr ----> HBr + NaHSO4

HBr + C2H5OH ----> C2H5Br + H2O

So ultimately:

H2SO4 + NaBr + C2H5OH ----> C2H5Br + NaHSO4 + H2O

Into the 1000ml flask, pour 50mls of ethanol. To this add 95grams of sodium bromide and swirl it to even distribute it. Measure out 100ml of concentrated sulfuric acid, and add 100ml of distilled water to it. This is very exothermic, so employ cooling during. Once the dilute sulfuric is sufficiently mixed, begin cooling it in the fridge or on an ice bath. It would also be wise to cool the flask of alcohol and sodium bromide. Once both are below room temperature, slowly add the dilute sulfuric into the 1000ml flask. You must go very slow, or else you will oxidize the bromine right out of the sodium bromide, which will cause a reduction in yield. It should take you anywhere from 10-30 minutes, the slower the better. A light tint of red or yellow is okay. Swirl it around constantly during the addition (or equip it with a magnetic stirrer). Once it has all been added, place it in a water bath, and attach a reflux condenser to the flask. Begin heating the water bath, and start running water through the condenser Be sure to note that ethyl bromide has an extremely low boiling point. Nothing less than the coldest water possible should be used, otherwise your product will simply boil away. To give you an example, hot water from a faucet will most certainly boil this. Reflux this for 1 hour. After this time, remove it from the oil bath (carefully) with the water still running. Let the air cool it down until it is no longer boiling.

If you have a separate flask for distillation, transfer it once it has stopped boiling. Do not let it cool to room temperature if you are transferring flasks. Make sure it has stopped boiling, as the ethyl bromide vapors are nasty for you. If you don't have to transfer flasks, then simply set it up for simple distillation Heat it with a water bath, keeping the bath at about 80C. The receiving flask should be kept in ice water, to minimize loss due to evaporation. Eventually, there will be an obvious clear layer above a milky white layer. Once it is mostly water coming over, stop the distillation. Add this to a separatory funnel, and shake it with distilled water - venting on occasion. Hang it upright and prepare a sodium bicarbonate solution. Remember, the bottom layer in the separatory funnel is the one you want. Drain the bottom layer off into your receiving flask, then dispose of the top water layer. Add the ethyl bromide to the separatory funnel and add the sodium bicarbonate solution to it. Shake it well, venting often. Drain and then repeat with distilled water once more.

Clean up your distillation set-up at this time. Use soap and water to get it all out, then rinse it with 96% ethanol. The ethyl alcohol will take most of the water out of the system. Once most of the alcohol has drained out, set it up for simple distillation one last time. Add a small amount of anhydrous magnesium sulfate to the distillation flask, and drain the lower ethyl bromide layer into the flask. Swirl it around, then begin heating it on a water bath. Keep the water bath below 50C and distill it dry. Yes, dry. There will be residual ethyl alcohol left in there, to keep it from actually becoming dry, since that boils at 78C. Keep the flask on the heat until nothing more drips from the condenser This is now your ethyl bromide. Store it in a fridge, or freezer. It evaporates very quickly. Theoretical yield. is 90g, I obtained roughly 50ml, which is equivalent to 73.5g, so a nice 82% yield.
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#4
Danke für die Aleitung für Ethybromid Wink . Hab aber jetzt mitbekommen, dass man die ganze Synthese statt mit dem Ethylbromid mit Ethyliodid machen kann, was wesentlich leichter zu beschaffen ist Tongue
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#5
Hab mir jetzt auch noch mal dein Synthese bezüglich Amobarbital angesehen. Da hast du Recht, statt 2 Mol des Ethylbromids gibst du jetzt ein Mol Ethylbromid und ein Mol Isoamylbromid hinzu und dann hast du dein gewünschtes Barbiturat  Rolleyes
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